Phosphuga atrata, found 5-V-2005 Netherlands, Flevoland, Roggebotzand in mixed woodland on path. Det leg and Photo E van Herk. This young adult specimen is not fully coloured yet; in a few days it would have become deep black. Size: 12 mm from jaws to distal end of elytra.
The brown one is no young specimen (juvenil) but P. atrata var. brunnea. This is a brown variation of the same species found in most populations. In some more often, in some more seldom.

Source: https://commons.wikimedia.org/wiki/File:Phosphuga_atrata_small.jpg

Phosphuga atrata, is a European carrion beetle that feeds on live snails, insects and earthworms, as well as on carrion. The beetle is up to 15mm long and has an elongated neck, which is used to reach into snail shells, which it sprays with a digestive fluid. Young beetles are brownish in color, older ones are black. The larvae are black and flattened and feed on snails as well. They pupate in the ground. Although they are widely distributed, they are seldom found, because they hunt at night and hide during the day, often under bark. When disturbed, they excrete a yellow fluid and retract their head under the shield. Order: Coleoptera, Family: Silphidae, Subfamily: Silphinae, Synonyms: Silpha atrata.